Few would know it by its official
designation, the Navy Type 1 Attack Bomber. The Allies called it the BETTY but
to the men that flew the airplane, it was popularly, but unofficially, the 'Hamaki,'
Japanese for cigar, in honor of the airplane's rotund, cigar-shaped fuselage.
The Japanese built more of them than any other bomber during World War II.
From the first day of war until after the surrender, BETTY bombers saw service
throughout the Pacific and Indian Oceans. Like its stable mate, Mitsubishi's
Zero Fighter the Hamaki soldiered on long after it became obsolete, even
dangerous, to fly wherever Allied interceptors prowled.

Click on Picture to enlarge

In July 1937, the new Mitsubishi
G3M bomber (Allied codename NELL) went into service in China. Only two
months later, the Navy issued a specification to Mitsubishi for a NELL
replacement. At that time, the requirements were unprecedented for a
twin-engine, land-based attack bomber: flying at a top speed of 398 kph
(247 mph) and an altitude of 3,000 m (9,845 ft), the new bomber had to
fly a distance of 4,722 km (2,933 miles) without a torpedo or equivalent
weight in bombs. When carrying an 800 kg (1,768 lb) torpedo or the same
weight in bombs, the Navy needed the bomber to fly at least 3,700 km
(2,300 mi).

To meet the requirements, a Mitsubishi
design team led by Kiro Honjo crafted an airplane called the G4M with fuel tanks
in the wings that were not resistant to explosion when punctured during combat.
These tanks were much lighter in weight than explosion-proof (also called
'self-sealing') gas tanks. The decision not to incorporate the heavier, safer
fuel tanks was necessary to meet the Navy's range requirements. Mitsubishi
incorporated this same design feature in the Zero, for the same reasons and with
the same results. Both aircraft had unprecedented range but they were also
extremely vulnerable to the machine gun and cannon fire from Allied fighter
aircraft. The BETTY was so prone to ignite that the Allies nicknamed it the
'flying lighter.'

Click on Picture to enlarge

The fuselage was streamlined but
rotund to allow space for a bomb bay within the wing center section and
to allow the 7 to 9-man crew to move about. About half the crew were
gunners who manned the defensive armament positions. Bomber crews flying
the NELL were virtually incapable of defending themselves from
concentrated fighter attacks, so Honjo paid special attention to this
aspect of the G4M. He incorporated 7.7 mm (.30 cal.) guns in the nose,
atop the mid-fuselage behind the cockpit, and on both sides of the
fuselage behind the wing. In the tail, he introduced a 20 mm cannon.
Although the G4M now had a more potent sting, Honjo again sacrificed
crew protection to the Navy's demands for great range. He omitted amour
plate.

Click on Picture to enlarge

The first G4M prototype left the factory in
September 1939 and made the trek to Kagamigahara Airfield for Mitsubishi's
Nagoya plant had no company airstrip. Kagamigahara was 48 km (30 miles) to the
north. Japan's newest and most advanced bomber made the trip, disassembled and
stacked on five ox-drawn farm carts, over unpaved roads! After arriving at the
airfield, the first G4M was reassembled and flown by test pilot Katsuzo Shima on
October 23, 1939. Initial results were impressive, but the Navy shelved the
bomber for a time in favor of a variant to be called the G6M1. Navy leaders
hoped that by increasing the number of defensive cannons, the G6M1 could become
a heavy escort fighter for other bombers but this diversion failed to live up to
expectations, and the Navy ordered the G4M1 into production. The U. S. Army Air
Corps conducted a similar experiment using a modified Boeing B-17 bomber
designated the B-40 but this idea too failed to survive operational testing and
was soon abandoned. The first production G4M rolled off the line in April 1941.
For the remainder of the war, the BETTY assembly line continued to run.

Click on Picture to enlarge

Built in larger numbers than any
other Japanese bomber and flown in action from Australia to the Aleutians,
the G4M Navy Type 1 Attack Bomber was the most famous Japanes bomber.
The Allied code name was "Betty".

Operationally, BETTY crews achieved
much in their first year of combat. They devastated Clark Field,
Philippine Islands, on December 8, 1941, and participated in sinking the
British battleships HMS "Prince of Wales" and HMS "Repulse" on December
10. They ranged across the length and breadth of the Pacific theatre,
attacking targets from the Aleutians to Australia. Against limited
fighter opposition, the lack of armour and self-sealing fuel tanks was
no hindrance. The savings in airframe weight allowed the G4M to attack
targets at unprecedented ranges. But as Allied fighter strength
increased, the BETTY began to reveal its fatal vulnerabilities. Admiral
Isoroku Yamamoto, architect of the Pearl Harbor attack, died on April
18, 1943, along with his entire staff when U. S. Army Air Corps P-38
Lightnings intercepted and destroyed the two BETTY bombers that carried
them. Six escorting Zeros flew guard but in a matter of seconds, the Air
Corps pilots shrugged off the escorting fighters and sent both BETTYs
crashing down in flames.

As the war dragged, improved bombers failed
to materialize so Mitsubishi fielded different versions of the G4M to fulfill
new missions, and to eliminate the various weaknesses in the basic design.
Front-line combat units operated many variants and sub-variants with different
engines and armament packages. The G4M2 was a complete redesign but it did not
overcome the airplane's vulnerability to Allied firepower. Mitsubishi tried
again to reduce the bomber's tendency to burn. The firm changed the wing to a
single-spar configuration and installed self-sealing fuel tanks with a capacity
about one-third less than earlier versions. The capacity dropped because of the
material inserted in the tank to block leaking fuel when gunfire perforated the
tank. Armour plate was also added to all crew positions and the tail turret was
redesigned. As a result of these modifications, the fuselage was shortened and
the center-of-gravity shifted forward. To re-balance the bomber, dihedral was
added to the horizontal stabilizer. This version was called the G4M Model 34.

Designation / Design Bureau

Mitsubishi G4M 'Betty'

Type

Seven crew land-based navy bomber

Engine

Two 1,800 hp ( 1343 kW ) Mitsubishi
MK4P Kasei 21 radial pistons

Maximum Speed

272 mph ( 438 km/h ) at 15,090 ft
(4600 m)

Climb Rate

32.4 minutes to reach 26,245 ft
(8000 m)

Ceiling

29,365 ft (8950 m)

Range

3,765 miles (6059 km)

Wingspan

70 ft, 4¼ in ( 21.44 m )

Length

48 ft, 6½ in ( 14.80 m )

Height

13 ft, 5½ in ( 4.10 m )

Wing Area

718.0 sq ft ( 66.7m2 )

Empty Weight

17,990 lb (8160 kg)

Loaded Take-off Weight

27,558 lb (12500 kg)

Armament (Defensive )

None

Weapons

2,205 lb (1000 kg) of bombs or one
1,764 lb (800 kg) torpedo

Total production 2,414

The G4M-
Allied reporting-name 'Betty' - was the main 'heavy' bomber of the Japanese
Navy during World War II. It was remarkable for its long range, but this
was achieved by depriving the aircraft of armour while providing it with
huge fuel tanks in the wings. Since the tanks were not self-sealing the
Betty was extremely vulnerable, tending to go up in flames whenever hit.
This led to its receiving the derisive nicknames 'One-Shot Lighter' and 'the
Flying Cigar'. Despite its range and speed, it was therefore - not
surprisingly - unpopular with its crews.

The G4M's single outstanding success was achieved at the start of the
Pacific War when, on 10 December 1941, only three days after Pearl Harbor,
G3M Nell's and G4Ms of the 22nd Air Flotilla sank two British capital ships
- the new battleship Prince of Wales and the old battlecruiser
Repulse - off the coast of Malaya. This action - sometimes referred to
as 'The Battle of the Gulf of Siam' - is more generally known as
'The Destruction of Force Z'.

Prince of Wales and Repulse were the first capital ships
ever to be sunk while at sea and free to manoeuvre. In fact, only three
other dreadnoughts were ever sunk by air attack under such conditions - the
Japanese giants Yamato and Musashi which were destroyed by US
carrier aircraft towards the end of the war,and
the Italian fast battleship Roma which wasattacked
(immediately after the Italian surrender) by German land-based aircraft
using radio-controlled glider-bombs.

The first attacks on Allied forces to be made following the
Guadalcanal landings were carried out by G4Ms flying from Rabaul. An attack
on the US transports by 26 Betties was to demonstrate to Allies and Japanese
alike the vulnerability of the G4M to anti-aircraft fire. At least 17
Betties were shot down. One aircraft damaged by gunfire made a suicide
crash on the transport George F. Elliott. The resulting fire
destroyed the ship - this was the only damage inflicted by Japanese air
attacks in reaction to the Allied landings.

G4Ms operated throughout the six months of fighting on Guadalcanal,
suffering heavy losses. By early 1943 the Japanese Navy had developed new
techniques for night torpedo attack. These were put into effect on the
night of 29/30 January 1943 in the Battle of Rennell Island, in which
Betties torpedoed and sank the heavy cruiser Chicago. G4Ms
repeatedly harassed US task groups in night attacks from this time until
almost the end of the war, occasionally inflicting heavy damage - for
example in February 1944 when a Betty torpedoed the Essex Class
carrier Intrepid after Task Force 58's raid on the Japanese base of
Truk in the Caroline Islands.

The G4M had been designed to meet a very demanding Navy specification
of 1938. Mitsubishi repeatedly advised the Navy that a four-engined design
would be preferable, but the Navy insisted on the restriction to two
engines. The G4M1 flew its first missions in China in May 1941.
Engine-power and fuel capacity were increased with the G4M2, the version
produced in the greatest numbers. In the G4M3 the balance of the design
was dramatically changed, with full protection being provided and fuel
capacity being drastically reduced.

In 1945 specially-modified G4Ms were employed to carry the Ohka
rocket-propelled piloted bomb. This development was in general a disastrous
failure, since the modified G4Ms when carrying the Okha were hopelessly
vulnerable to fighter attack - although if the G4M succeeded in launching
the Okha within range of allied ships the weapon then often proved
devastating.

Total production of the G4M was 2,479 - a remarkably high figure for a
Japanese medium or heavy bomber.

The Mitsubishi G4M 'Betty' Bomber

The Mitsubishi G4M

Role

Twin-engine medium bomber

Manufacturer

Mitsubishi

Designed by

Kiro Honjo

First
flight

23 October 1939

Introduced

June 1941

Retired

1945

Primary user

IJN Air Service

Number built

2,435

The Mitsubishi G4M or 一式陸攻 Ichishiki rikujō kōgeki ki,
Isshikirikkō ("Type 1 land-based attack aircraft") was the main
twin-engine, land-based bomber aircraft used by the Imperial Japanese Navy
Air Service in World War II. The Allies gave the G4M the identification
name of Betty,[1]

Design And Development

The G4M had a long range and high-speed at the time of its
introduction. However, it was known for its poorly-protected fuel tanks,
which caused Allied fighter pilots to give it the derisive nicknames
"one-shot lighter", "flying Zippo" and "flying cigar". Similarly, pilots
of the Imperial Japanese Navy called the G4M the "Type One Lighter" and
Hamaki (Cigar). This was due to the fact that on many occasions, it
was used for low-altitude torpedo attacks where its performance advantages
were negated. The "Betty"'s relatively-large size made it a large target
to shoot at, and the simplified approach path on a torpedo run to attack a
ship, meant for a generally easy interception.

When used for medium- to high-altitude bombing against stationary
targets like a supply depots, seaports, or airfields, "ease of
interception" was another matter entirely. Using its long range and high
speed, the G4M could appear from any direction, and then be gone before
many fighters could intercept them. The 20 mm cannon in the tail turret
was much heavier armament than commonly installed in bombers, making dead
astern attacks very dangerous. Sometimes, assuming they did not catch fire
in the first place, G4Ms also proved to be able to remain airborne despite
being badly shot up. For example, after 751 Kokutai's attack during
the Battle of Rennell Island, three out of four survivors (of eleven
aircraft that went to attack) returned flying on one engine only. Near the
end of the war the "Betty" was used as a common kamikaze-carrying and
launching platform, and was the usual aircraft for carrying the Ohka
kamikaze rocket aircraft.

Production

Total production of G4M1 Model 11: 1172 examples including
prototypes.

Early
production G4M1s of Kanoya Kokutai with the original shape tail cones

The G4M was similar in performance and missions to other
contemporary twin-engine bombers such as the German
Junkers Ju 88
and Heinkel He 111, the
North American B-25 Mitchell, and the American
Martin B-26
Marauder. These were all commonly used in the anti-shipping role, and
all but the B-25 were used as torpedo-bombers. The G4M Model 11 was
prominent in attacks on Allied shipping in the 1941 to early 1944
time-frame, but beyond that time, it was increasingly the easy prey of the
ever-improving enemy fighters.

The G4M's baptism by fire occurred September 13, 1940 in Mainland
China, when 27 Bettys and Mitsubishi C5M1 of 1st Rengo Kokutai
(a composite force including elements of Kanoya and Kizarazu
Kokutais) departed from Taipei, Omura and Cheju to attack Hankow. The
bombers and reconnaissance aircraft were escorted by 13 Mitsubishi A6Ms of
12st Kokutai led by Navy Lt. Saburo Shindo. A similar operation
occurred in May 1941. In December 1941, 120 Taiwan-based G4Ms of 1st
Kokutai and Kanoya Kokutai belonging to the 21st Koku Sentai
crossed the Luzon Strait en route to bombing the Philippines, the
beginning to widespread Southeast Asia operations.

As torpedo bombers, the G4M's most notable use was in the sinking of
Prince of Wales and the Repulse off the coast of Malaya on
December 10 1941. They carried out the attacks alongside the older
Japanese bombers, the Mitsubishi G3M "Nells" who were doing high-level
bombing runs. The Prince of Wales and the Repulse were the
first two capital ships ever to be sunk exclusively by air attack during a
war, while at sea. Those bomber crews were a handful of selected Imperial
Japanese Naval Air Force (IJNAF) aviators in prewar Japan, who had skills
not only in torpedo-attacking at less than 30 ft high but also in being
able to navigate long range flight over the ocean to spot a pinpoint
target moving fast on the sea. The same squadrons in Kanoya AG (751 Ku),
Genzan AG (753 Ku) and Mihoro AG (701 Ku), which sunk the British capital
battle ships, later staged an extended series of attacks against American
ships and land targets in Battle of Guadalcanal in the Solomon Islands,
late 1942.

On August 8 1942, the 2nd day of US Marine's landing at Guadalcanal,
IJNAF's 23 G4M1s conducted a torpedo attack against American ships at
Lunga point, Guadalcanal. 18 of the attacking G4M1s were lost, due to
extraordinarily heavy antiaircraft fire and air cover from F4F fighters.
In all, 18 Japanese crews of approximately 120 aviators were missing in
the beginning of the months. Over 100 Japanese G4M1s and their best crews
with no substitute were thoroughly lost in the following battles of
Guadalcanal, between August and October, 1942.[2]
In two days of the Battle of Rennell Island on January 29 and 30, 1943, 10
out of 43 Japanese G4M1s were lost in the night torpedo-attacks, again to
American anti-aircraft fire. About 70 Japanese aviators including Lt Cdr
Higai were killed in action.

Probably the best-known incident involving a G4M during the war was
the attack resulting in the death
of Isoroku Yamamoto. The G4M with tail number T1-323, which was
carrying the IJN Admiral Isoroku Yamamoto, was attacked and shot down by
American P-38 Lightnings on April 18,
1943.

The G4M Model 11 was replaced by Models 22,22a/b,24a/b,25,26
and 27 after June 1943, following service in New Guinea, the
Solomons, and the South Pacific area, in defense of Marianas and finally
in Okinawa, with field modifications resulting in the Model 24j
which carried suicide flying bombs Yokosuka MXY7 Ohka Model 11
beginning on 21 March 1945, with disastrous results due to heavy Allied
fighter opposition.

Following the loss of Okinawa, G4Ms constituted the main weapon of
the land-based Japanese naval bomber force, consisting of 20 Kokutais when
at war's end, including the testing air group equipped in 1944-45 with the
latest version G4M3 Model 34 and 36, arriving too late to
change the course of the war.

As part of the negotiations for the surrender of Japan, two
demilitarized G4Ms, given the call-signs Bataan 1 and Bataan 2 were sent
to Ie Shima carrying the first surrender delegations as the first leg of
their flight to Manila.

In 1945, Indonesian guerrillas captured numerous ex-Japanese air
bases including Bugis Air Base in Malang (repatriated 18 September
1945). Several G4Ms were seized and flown by the Indonesians. Most of the
aircraft were destroyed during 1945–1949 when the former Dutch East Indies
and the Netherlands were engaged in a military conflict in Indonesia.

Variations

G4M1

G4M1 Prototypes

Japanese Navy land Based Bomber Type 1. Two prototypes built.

G4M1 Model 11

Japanese Navy Land Attack Bomber Type 1. The first bomber model
of series, with 1,530 hp (1,140 kW) Mitsubishi MK4A Kasei Model
11 engines driving three-bladed propellers. Following modifications were
made during the production:

March 1942: The first aircraft (241st production example) fitted
with MK4E Kasei Model 15 engines with larger superchargers for
better high altitude performance, became standard in August 1942 from
406th aircraft onwards. These MK4E-engined aircraft have been often,
erroneously, referred as the G4M1 Model 12.

The base model, the first production example completed in July
1943. Introduced bulged bomb bay doors from 65th aircraft onwards, and
an optically flat panel in the nose cone from the 105th aircraft
onwards.

Modified Model 22, MK4T Kasei 25 1,800 hp (1,340 kW) engine, with
bulged bomb bay doors as standard for larger bomb capacity. Externally
distinguishable from the Model 22 by a carburetor air intake on the top
of the engine cowling.

G4M2a Model 24 Ko/Otsu

Armament similar to Model 22 Ko/Otsu respectively.

G4M2a Model 24 Hei

Modified 24 Otsu, with one 13 mm Type 2 machine gun
mounted in tip of the nose cone, radar antenna relocated from that
position to above the nose cone.

Special version for the transport of the ramming attack bomb
plane Kugisho/Yokosuka MXY-7 Ohka ("Baka") Model 11, conversions
of G4M2a Models 24 Otsu and 24 Hei. Had armour protection
for the pilots and fuselage fuel tanks.

MXY11 Yokosuka Navy Type 1 Attack Bomber

Ground Decoy Non-flying replica of Mitsubishi G4M2 developed by
Yokosuka

G4M3

G4M3 Model 34

Redesigned G4M2 with added self-sealing fuel tanks, improved
armor protection and an entirely new tail gunner's compartment which was
quite similar to that of late model American B-26 Marauders. Wings were
also redesigned and horizontal tail plane was given dihedral. Armed with
two Type 92 7.7 mm machine guns in nose cabin and in both side
positions, and one type 99 model 1 20 mm cannon in dorsal turret and
tail. Entered production in October 1944 in G4M3a Model 34 Ko
form with 20 mm cannon in side positions instead of machine guns.

G6M1

G6M1 Japanese Navy Long Range Heavy Fighter Type 1

Initial model of the series, armed with Type 99 20 mm cannons
between each side of fuselage and in tail, one 7.7 mm machine gun in
nose cabin and one 30 mm cannon in front ventral position. Thirty built.

Green, William. Famous Bombers of the Second
World War. London: Macdonald and Jane's Publishers Ltd., 1975.
ISBN 0-356-08333-0. (2nd edition of 1959 book, reprinted at least
twice: 1976 and 1977)

Horodyski, Joseph M. "British Gamble In Asian
Waters". Military Heritage. December 2001. Volume 3, No. 3:
pp. 68–77 (sinking of the British battleship Prince of Wales
and battlecruiser Repulse by Japanese on 10 December 1941
upon U.S. entry into World War Two).